Schaublin 125-CNC retrofit.

Thanks a lot. So with Ethercat drives, do you again have the option of having the drive close just the velocity loop, or both velocity and position loops?

I get the tuning. You need to tune the system to the axis inertia. Actually I did a course on motion control, and we worked through the sizing of drives based on inertia matching. I need dig into that again, and work out what motors would be needed.
Mark

that depends on the drive, all that i know have all options (torque, veloctiy, position and all combinations of them...

but the advantage of the underlaying transport system (ethercat) is, that you are able to sync the execution times from the drives. (distributed clocks, the exact timestamp when the drive should fetch and put his information from/to the bus.)

So you can also do cyclic position mode/control. for Examble an Beckhoff AX5000 does his position control at an cycle time of about 62.5µs equal to usually linuxcnc servo period of 1ms... if such an controller is well tuned (right inertia, resonace filters etc. ) that are mega precisious and fast Axis.

Wasn't there a servo drive called stimbl ( may be spelled wrong ) ? Think Andy P an Skunkworks were trying those drives out with good results. Thought it used ethercat .

I would never start tuning as system with everything attached. I make too much errors and had the Z axis oscillating in the beginning and it was not funny.

I never used a step dir cause I didn’t have system that supported this. But I seem I also believed this myth. As far as I understood with analog control you tune the drives to match a certain speed to a voltage and then tune LinuxCNC to stay on the planned path.

With my Chiron I was Lucky cause the drives were tuned and
I did my tuning without the belts and it was quite good after I realised that I had an error in calculating the max acceleration. BUT I had the acceleration read out from the old parameters and just needed to convert it the the units used by LinuxCNC.

Using velocity mode, tuning for load inertia is done in the drive so using the existing
(tuned) drives means only position mode tuning (chiefly FF1 and P) is needed

as PCW told
if you have an good tuned stiff velocity loop and no mechanical play then for position controll there is only a bit of P neccesary. (and FF1 for fine tuning of analog setpoint, in an digital drive system this is normaly 1.0)

But tuning an Velocity / Torque loop without load is nearly impossibel. If you get an todays velocity loop with acceleration feedforward, reconance filters, highpass, inertia calculated velocity observer etc. proper tuned, then the following error with only velocity loop should be +- zero.